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A flyback diode (also known as a freewheeling diode or snubber diode) is used to protect circuits from inductive kickback, which occurs when the current flowing through an inductive load (like a motor or relay coil) is suddenly interrupted.
Here’s how it works:
- When the current is flowing through the inductor normally, the diode doesn’t conduct because it’s reverse-biased.
- When the switch opens and the inductor tries to generate a high voltage (inductive kickback), the diode becomes forward-biased and provides a path for the current to circulate through the inductor.
This circulating current allows the energy stored in the magnetic field of the inductor to dissipate slowly, preventing the high voltage from building up and causing damage.
In simple terms, the flyback diode "catches" the sudden surge of current and gives it a safe path to flow through, rather than letting it cause harm to the rest of the circuit.
Here’s how it works:
- Inductive Kickback: When current is flowing through an inductor (like a coil), it creates a magnetic field around it. If the current is suddenly turned off (e.g., a switch opens), the inductor resists this sudden change in current by generating a high voltage across its terminals. This is due to the Lenz's Law (which states that the change in magnetic flux through the inductor causes an opposing voltage). This high voltage can be large enough to damage other components in the circuit, like transistors or microcontrollers.
- Role of the Flyback Diode: The flyback diode is connected in parallel with the inductive load, but in the reverse direction (i.e., its cathode is connected to the positive side of the load, and the anode to the negative side).
- When the current is flowing through the inductor normally, the diode doesn’t conduct because it’s reverse-biased.
- When the switch opens and the inductor tries to generate a high voltage (inductive kickback), the diode becomes forward-biased and provides a path for the current to circulate through the inductor.
This circulating current allows the energy stored in the magnetic field of the inductor to dissipate slowly, preventing the high voltage from building up and causing damage.
- Result: By allowing the energy in the inductor to be released gradually, the flyback diode prevents overvoltage spikes that could damage sensitive components in the circuit.
In simple terms, the flyback diode "catches" the sudden surge of current and gives it a safe path to flow through, rather than letting it cause harm to the rest of the circuit.